EP0247207B1

EP0247207B1 - Injection control method and injection controller in an injection molding machine

Info

Publication number: EP0247207B1
Application number: EP86906956A
Authority: EP
Inventors: Hiromasa Otake
Original assignee: Fanuc Corp
Current assignee: Fanuc Corp
Priority date: 1985-11-29
Filing date: 1986-11-29
Publication date: 1991-01-30
Anticipated expiration: 2006-11-29
Also published as: EP0247207A1; US4816196A; JPH0344890B2; JPS62127221A; KR880700727A; KR940011359B1; DE3677381D1; WO1987003247A1; EP0247207A4

Abstract

A method and apparatus for controlling the operation of an injection molding machine by a servo motor that is controlled by a numerical control device. In order to control the injection speed and the pressure maintenance depending upon the time, pulses are distributed to the servo motor until the point of pressure maintenance completion is reached after the injection speed control and pressure maintenance control at preset times are finished, and then the follow-up is carried out to complete the injection control.

Description

Technical Field.

The present invention relates to an injection - molding machine, and more particularly, to a method and an apparatus for controlling injection of an injection - molding machine, in which the injection of the injection-molding machine is controlled by means of a numerical control unit.

Background Art

Injection control in an injection-molding machine may be effected by two control methods, as shown in Figs. 4 and 5. Namely, in a system of the type shown in Fig. 4, speed control is performed from an injection start position, and, when a screw reaches a switching position for hold, the speed control is changed over to hold pressure control. Thereupon, hold is performed for a predetermined period of time, and a metering block in the next stage is entered. According to the system of Fig. 5, injection control is performed for a predetermined time after the start of injection, and, when the predetermined time for the injection control elapses, the injection control is changed over to the hold pressure control. When the hold time terminates, the metering block in the next stage is entered.
Conventionally, in controlling an injection - molding machine by means of a numerical control unit (hereinafter referred to as NC unit), the system of Fig. 4, not the system of Fig. 5, has been used. However, if the screw cannot inject resin at a predetermined injection speed and cannot, therefore, reach the switching position for hold within a normal required injection time, on account of too high viscosity of the resin or any other reasons, the time required for the execution of an injection cycle is extended, thus lowering the efficiency of production. Also, the screw cannot follow up an output command, for use as a speed command, so that an error of a command for movement, compared with an actual screw position, is stored in an error register in the NC unit. If the value of the error reaches or exceeds a predetermined level, the NC unit stops pulse distribution, thereby possibly stopping the whole injection-molding machine in an unexpected manner.
The article 'Grundlagen der Prozessteuerung beim Spritzgiessen', pages 74-80 of 'Kunststoffe', Vol. 61, no. 2 (1971) discloses the effect of differing pressures in processes as shown in Figs. 4 and 5 discussed above. However, no solution to the problem of unwanted stoppage of the injection-molding machine is presented.
It is an object of the present invention to provide a method of injection control for an injection-molding machine by means of an NC unit, whereby the aforementioned drawbacks of the prior art are eliminated.
According to one aspect of the present invention, injection is performed by means of a servomotor controlled by a numerical control unit including a servo circuit responsive to pulses distributed from a processing unit, the method comprising the steps of driving the servomotor so as to move a screw at a predetermined injection speed for injection-speed control towards a changeover position, effecting changeover to hold-pressure control at the latest after the injection-speed control has been executed for a predetermined time, distributing pulses so as to drive the screw towards a hold pressure end position, compulsorily distributing pulses corresponding to the screw reaching the hold end position after the hold pressure control has been executed for a predetermined time, if the screw has not in fact reached that position, and performing a follow-up operation such that a value stored during the pulse distribution in an error register in the servo circuit, corresponding to whether the screw has reached a desired end position, is reduced to zero, thereby completing the injection control.
According to another aspect of the invention there is provided an injection control apparatus for an injection-molding machine which performs injection by means of a servomotor controlled by pulses distributed from a numerical control unit, the apparatus including: an injection-speed control means for controlling the injection speed, a first timer for detecting the passage of a predetermined time after the start of injection, a hold pressure control means adapted to perform hold pressure control at the latest when the preset time of the first timer is up, a second timer for detecting the passage of a predetermined time after the start of the hold pressure control, and follow-up means adapted to perform compulsory pulse distribution indicating that the position of the screw has reached a hold pressure end position and to perform a follow-up operation such that a value stored in an error register during the pulse distribution, corresponding to whether the screw has reached a desired end position, is reduced to zero, when the preset time of the said second timer is up.
In embodiments of the invention, injection control can be performed on the basis of the time elapsed after the start of injection. Injection can be controlled in a time-based manner, even in an injection-molding machine which is controlled by an NC unit. The duration of injection cycle is limited, since even if a servomotor, for use as a drive source for the injection, cannot inject resin at a predetermined speed so that the screw cannot reach a switching position for hold, for any reason, the control mode is switched to hold pressure control and the second timer is actuated when the preset time of the first timer is up. When the preset time of the second timer is up, pulse distribution is performed compulsorily corresponding to the screw reaching the hold pressure end position, and the follow-up operation is carried out. Accordingly, the pulse distribution for a block for the movement command, out of commands for injection and hold, is completed, so that the NC unit can proceed to a metering cycle in the next stage. Thus, the NC unit can be operated efficiently, without stopping the whole injection-molding machine.
Further embodiments of the invention are defined in the dependent claims.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a block diagram showing the principal part of an embodiment of the present invention;
Figs. 2 and 3 are flow charts illustrating operation of the embodiment of Fig. 1; and
Figs. 4 and 5 are diagrams for illustrating injection control.

Fig. 1 is a block diagram showing the principal parts of an embodiment of the present invention, in which numeral 1 denotes an NC unit, and symbol M designates a servomotor which drives, for injection, an injection axis or screw of an injection-molding machine in the axial direction. The servomotor M is provided with a position detector P for detecting the position, speed, etc., of the screw. The NC unit 1 includes a microprocessor (hereinafter referred to as CPU) 2 for NC, and a CPU 3 for programmable controller (hereinafter referred to as PC). The PCCPU 3 is connected with a ROM 5 which stores a sequence program for the injection-molding machine. The NCCPU 2 is connected with a ROM 7, which stores a control program for generally controlling the injection-molding machine, and with a servo-control circuit 9 for controlling the drive of the servomotor M, through a servo-interface 8. The output of the servo-control circuit 9 is amplified by means an amplifier 12, and is used to drive the servomotor M.
In Fig. 1, although the servo-control circuit 9 and the servomotor M for the injection axis are only shown, the servo-interface 8 is also connected with servo-control circuits for servomotors which are associated with a clamp axis, used to drive a die-clamping mechanism, and a metering axis for rotating the screw. Fig. 1 shows the servo-control circuit 9 and the servomotor M for the injection shaft only.
Numeral 6 denotes a nonvolatile RAM which, including a backup power source, stores programs for controlling individual operations of the injection-molding machine, various set values, parameters, etc. Numeral 11 denotes a manual- data input device with a CRT display (hereinafter referred to as CRT/MDI), which is connected to a bus-arbiter controller (hereinafter referred to as BAC) 4 through an interface 10. The BAC 4 is connected with the respective buses of the NCCPU 2, the PCCPU 3, and the nonvolatile RAM 6. The bus to be used is selected by the BAC 4.
Referring now to the operational flow charts of Figs. 2 and 3, the operations of the present embodiment, arranged in the aforesaid manner, will be described.
First, the CRT/MDI 11 sets various conditions for an injection cycle, such as the injection speed for each injection step, injection-speed changing position, position for a changeover from injection-speed control to hold pressure control, injection time, hold time, torque-limit value used to control the pressure for hold, rapid-feed rate value used in compulsory pulse distribution, as mentioned later, etc. These conditions are stored into the nonvolatile RAM 6.
At the start of operation, the NCCPU 2 reads out, through the BAC 4, an injection-speed control program stored in the nonvolatile RAM 6. Based on this program, the NCCPU 2 performs pulse distribution according to the injection speed for each injection step, in order to accomplish injection-speed control. At the start of a first step of injection, the CPU 2 delivers a pulse-distribution start signal and an M1 code to the PCCPU 3 through the BAC 4, and stores them into the nonvolatile RAM 6. The M1 code is indicative of an injection-speed control block being executed. When the PCCPU 3 reads and detects the pulse - distribution start signal from the nonvolatile RAM 6, it starts an injection high-timer T1, used to measure an injection-speed control time, and starts an injection sequence on detection of the M1 code (Step S1). Then, the PCCPU 3 repeatedly determines whether or not the preset time of the injection high-timer T1 is up (Step S2), and whether or not a signal indicative of a completion of pulse distribution up to a switching point for hold is delivered from the NCCPU 2 (Step S3).
If the NCCPU 2 finishes the pulse distribution up to the switching point for hold before the preset time of the injection high-timer T1 is up, and when the nonvolatile RAM 6 is stored with a pulse-distribution end signal, the PCCPU 3 reads this signal from the nonvolatile RAM 6 through the BAC 4. Thereupon, the PCCPU 3 delivers an M1-code end signal FIN, indicative of a completion of the injection-speed control block, and stores the signal FIN into the nonvolatile RAM 6 (Step S4). On reading the M1-code end signal from the nonvolatile RAM 6, the NCCPU 2 reads out a control program for a hold pressure control block stored in the nonvolatile RAM 6. Then, the NCCPU 2 starts hold pressure control in accordance with this program, and stores the nonvolatile RAM 6 with an M2 code, which is indicative of an entry into the hold pressure control. Thereupon, the PCCPU 3 identifies the M2 code, starts a hold pressure timer T2, and delivers a torque-limit value corresponding to a set hold pressure stored in the nonvolatile RAM 6. At the same time, the PCCPU 3 causes the NCCPU 2 to drive the servomotor M so that the output torque of the motor M is restricted to a value corresponding to the torque-limit value, thus performing hold pressure control in a manner such that the set hold pressure is applied to resin (Step S5). During the hold pressure control, the NCCPU 2 executes pulse distribution for hold pressure control. On completion of the pulse distribution, the NCCPU 2 delivers a second pulse-distribution end signal. Then, the PCCPU 3 determines whether or not the preset time of the hold pressure timer T2 is up (Step S6). If it concludes that the preset time is up, the PCCPU 3 further determines whether or not the nonvolatile RAM 6 is stored with the pulse-distribution end signal for hold from the NCCPU 2 (Step S7). If it detects a delivery of the second pulse-distribution end signal from the NCCPU 2, the PCCPU 3 delivers an M2-code end signal FIN to the NCCPU2 through the nonvolatile RAM 6, concluding that the hold pressure control block is finished (Step S8). On receiving the M2- code end signal, the NCCPU 2 starts a metering cycle as a block next to the hold block.
On the other hand, if the injection high-timer T1 is up, in Step S2, before the pulse-distribution end signal, indicative of a completion of the pulse distribution up to the switching position for hold pressure control in the injection-speed control block, is delivered from the NCCPU 2, the PCCPU 3 starts a sequence of hold operations. While limiting the torque of the servomotor M on the basis of the torque-limit value corresponding to the hold pressure set in the nonvolatile RAM 6, the PCCPU 3 drives the motor and starts the hold pressure timer T2 (Step S9). Thus, if the screw fails to reach the switching position for hold within a normal required injection time set by the injection high-timer T1, for any reason, the operation mode is changed compulsorily over to the hold pressure control when the set time is up.
Subsequently, the PCCPU 3 determines whether or not the pulse-distribution end signal, indicative of completion of the pulse distribution up to the switching position for hold, is delivered from the NCCPU 2 (Step S10), and whether or not the preset time of the hold pressure timer T2 is up (Step S11). If the preset time of the hold pressure timer T2 is up before the signal indicative of the completion of the pulse distribution up to the switching position for hold, that is, if the preset time of the hold pressure timer T2 is up before the screw reaches the switching position for hold, the PCCPU 3 starts a follow-up function of the numerical control unit 1, and at the same time, turns on a dry-run function of the unit 1, and starts or turns on a rapid-feed-rate output operation (Step S12). More specifically, the NCCPU 2 reads out a value in an error register which stores therein the difference between a speed command value in the servo-control circuit 9 and a signal from the position detector P attached to the servomotor M. Then, the NCCPU 2 delivers a pulse output such that the read value becomes zero, thereby performing follow-up operation. Since a dry-run-on signal is on, the remaining distribution pulses are delivered from the NCCPU 2 to the error register at a speed set by the rapid-feed rate. Thus, although the screw position has not reached the switching point for hold yet, the pulse distribution is performed compulsorily (because the NC unit cannot proceed to the next block without finishing the pulse distribution for the block concerned). In this manner, although the screw position is not shifted to the switching position for hold, the pulse distribution up to the switching position for hold is accomplished compulsorily, and the follow-up operation is achieved so that the value in the error register becomes zero, that is, as if the screw had reached the switching position for hold. In consequence, the value in the error register cannot exceed a predetermined value, and the injection-molding machine cannot be stopped wholly. If the PCCPU 3 detects a delivery of a follow-up end signal for the M1 block (injection-speed control block) from the NCCPU 2 (Step S13), it delivers the M1-code end signal (Step S14).
At the time of delivery of the M1-code end signal, the NCCPU 2 further starts to execute the M2 block (hold pressure control block), and the follow-up operation is also performed during the execution of this block, in the manner as aforesaid. Thereafter, a follow-up end signal for the M2 block from the NCCPU 2 is applied to the PCCPU 3 (Step S15), whereupon the CPU 3 turns off the follow-up function, dry-run function, and rapid-feed-rate output operation of the numerical control unit 1 (Step S16), and delivers an M2- block (pressure-control-block) end signal FIN to the NCCPU 2 (Step S17). On reception of this end signal FIN, the NCCPU 2 proceeds to the metering cycle in the next stage.
If the end signal indicative of a completion of the pulse distribution up to the switching position for hold is applied from the NCCPU 2 to the PCCPU 3, in Step S10, before the preset time of the hold pressure timer T2, which has started after the changeover to the hold pressure control, is up, the PCCPU 3 delivers the M1-code end signal to the NCCPU 2 (Step S18), while the NCCPU 2 starts to control the hold block, and also delivers the M2 code, indicative of the execution of the hold pressure control, to the PCCPU 3. On identifying this M2 code, on the other hand, the PCCPU 3 starts to control a hold operation sequence, and reads and delivers the torque-limit value which, corresponding to the set hold pressure, is stored in the nonvolatile RAM 6. Thus, the PCCPU 3 drives the servomotor M, for hold pressure control, so that the output torque of the motor is restricted to the delivered torque-limit value (Step S19). Then, the CPU 3 determines whether or not the preset time of the timer T2 is up (Step S20). If it concludes that the preset time of the timer T2 is up, the CPU 3 further determines whether or not the pulse distribution end signal, in the hold block, is being delivered from the NCCPU 2 (Step S21). If it detects the delivery of the signal, the CPU 3 delivers the M2- code (hold-pressure control) end signal, and proceeds to the metering cycle in the next stage.
If it is concluded, in Step S21, that the pulse distribution end signal is not detected, though the preset time of the hold pressure timer T2 is up, that is, if the pulse distribution in the hold is not finished, the follow-up function, dry-run function, and rapid-feed-rate output operation are turned on, just as in Step S12. Thus, the pulse distribution is executed compulsorily, and the follow-up operation is performed to reduce the value in the error register to zero (Step S23). Thereafter, processes of Steps S15 to S17 are executed.
If it is concluded in Step S7, moreover, that the pulse distribution for hold pressure is not completed even after the preset time of the hold pressure timer T2 is terminated during the hold pressure control in the hold pressure block, after the end of the injection-speed control, the process of Step S23 and other processes following the same are executed. Thus, the hold pressure control is completed compulsorily, and the metering cycle is entered in the next stage.
In the embodiment described above, the changeover from the injection-speed control to the hold pressure control is based on the screw position or time elapsed, whichever is the earlier, and the changeover from the hold pressure control to the metering cycle is based only on the time elapsed.
Alternatively, however, both changeovers, to the hold cycle and to the metering cycle, may be effected on the basis of the time only, without using the method of changeover to hold or metering by detecting the screw position. In this case, the processes of Steps S3 to S8, S10, and S18 to S23, shown in the operational flow charts of Figs. 2 and 3, are unnecessary: Step S1 is followed by Step S2, in which termination of the preset time of the timer T1 is awaited, whereupon Step S9 is entered. Step S9 is followed by Step S11, in which termination of the preset time of the hold pressure timer T2 is awaited. When the preset time of the hold pressure timer T2 is up, the processes of Step S12 to S17 are executed. In general, either, both or neither of the changeovers may be effected on the basis of the elapsed time only.

Claims

1. A method of injection control for an injection-molding machine in which injection is performed by means of a servomotor (M) controlled by a numerical control unit (1) including a servo circuit (9) responsive to pulses distributed from a processing unit (2), the method comprising the steps of driving the servomotor (M) so as to move a screw at a predetermined injection speed for injection-speed control towards a changeover position, effecting changeover to hold-pressure control at the latest after the injection-speed control has been executed for a predetermined time (T1), distributing pulses so as to drive the screw towards a hold pressure end position, compulsorily distributing pulses corresponding to the screw reaching the hold end position after the hold pressure control has been executed for a predetermined time (T2), if the screw has not in fact reached that position, and performing a follow-up operation such that a value stored during the pulse distribution in an error register in the servo circuit (9), corresponding to whether the screw has reached a desired end position, is reduced to zero, thereby completing the injection control.

2. An injection control method according to claim 1, wherein, if the screw reaches the changeover position for hold during the injection-speed control before the said predetermined injection-speed control time (T1) terminates, the control mode is changed over to hold pressure control immediately (step S4).

3. An injection control method according to claim 1 or 2, wherein, if the screw position reaches the hold end position during the hold pressure control before the said predetermined hold pressure control time (T2) terminates, injection control is considered to have been finished and the next process is entered.

4. An injection control method according to claim 1 or 2, wherein, if the predetermined hold pressure control time (T2) terminates before the screw position reaches the hold end position, injection control is considered to have been finished and the next process is entered (steps S6, S7; S20, S21

5. An injection control method according to any preceding claim, wherein the or each follow-up operation and the corresponding pulse distribution are performed at high speed.

6. An injection control apparatus for an injection-molding machine which performs injection by means of a servomotor (M) controlled by pulses distributed from a numerical control unit (1), the apparatus including: an injection-speed control means for controlling the injection speed, a first timer (T1) for detecting the passage of a predetermined time after the start of injection, a hold pressure control means adapted to perform hold pressure control at the latest when the preset time of the first timer (T1) is up, a second timer (T2) for detecting the passage of a predetermined time after the start of the hold pressure control, and follow-up means adapted to perform compulsory pulse distribution indicating that the position of the screw has reached a hold pressure end position and to perform a follow-up operation such that a value stored in an error register during the pulse distribution, corresponding to whether the screw has reached a desired end position, is reduced to zero, when the preset time of the said second timer (T2) is up.

7. An injection control apparatus according to claim 6, further comprising detecting means for detecting the quantity of pulse distribution to the servomotor (M), the hold pressure control means being further adapted to perform the hold pressure control when the said detecting means detects a completion of pulse distribution up to a changeover position for hold before the preset time of said first timer (T1) is up.

8. An injection control apparatus according to claim 7, wherein the numerical control unit (1) is adapted to terminate injection control when the said detecting means for detecting the quantity of pulse distribution detects the completion of the pulse distribution up to the hold pressure end position before the preset time of the said second timer (T2) is up.

9. An injection control apparatus according to claim 6, wherein the numerical control unit (1) is adapted to terminate injection control when the preset time of the said second timer (T2) is up.

10. An injection control apparatus according to any of claims 6 to 9, wherein the follow-up means performs the pulse distribution at a predetermined speed to execute the follow-up operation.